LED array module

ABSTRACT

The invention describes a light emitting diode array module (30) comprising a plurality of light emitting diode structures (10a, 10b), wherein the light emitting diode structures (10a,10b) are arranged such that there is an optical cross talk between the light emitting diode structures (10a, 10b) during operation of the light emitting diode array module (30), wherein at least a first light emitting diode structure (10a) of the plurality of light emitting diode structures (10a, 10b) is characterized by a first color, and wherein at least a second light emitting diode structure (10b) of the plurality of light emitting diode structures (10a, 10b) is characterized by a second color different than the first color, wherein the first color, the second color and the optical cross talk between the light emitting diodes are arranged to provide a predefined light distribution in a reference plane (40) perpendicular to an optical axis (50) of the light emitting diode an-ay module (30). The invention further describes a lighting device comprising one or more LED array modules (30).

FIELD OF THE INVENTION

The invention relates to a light emitting diode (LED) array module. The invention further relates to a lighting device comprising one or more LED array modules.

BACKGROUND OF THE INVENTION

The human eye is very sensitive with respect to variations in a light distribution or illumination pattern provided by a light source. Homogeneity of the correlated color temperature of the light distribution provided by a lighting module is therefore an important quality criterion. Especially lighting modules comprising a multitude of light emitters like light emitting diode (LED) structures require a careful selection of these LED structures in order to enable a homogeneous distribution of the color and especially of the correlated color temperature in a defined sector of the space illuminated by the lighting modules.

US 2012/0106145 A1 discloses an operating light which includes at least one first radiation source, which is suitable for producing light with locally different, especially radially outwardly decreasing color temperature distribution in a plane extending at right angles to the work area.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a light emitting diode (LED) array module with improved distribution of the color especially the correlated color temperature.

The invention is described in the independent claims. The dependent claims comprise preferred embodiments.

According to a first aspect a light emitting diode (LED) array module is provided. The LED array module comprises a plurality of light emitting diode structures. The light emitting diode structures are arranged such that them is an optical cross talk between the light emitting diode structures during operation of the light emitting diode array module. At least a first light emitting diode structure of the plurality of light emitting diode structures is characterized by a first color or flux. At least a second light emitting diode structure of the plurality of light emitting diode structures is characterized by a second color different than the first color. The at least second light emitting diode structure of the plurality of light emitting diode structures may alternatively or in addition be characterized by a second flux different than the first flux. The first color or the first flux, the second color or the second flux and the optical cross talk between the light emitting diodes are arranged to provide a predefined light distribution and preferably a predefined color distribution in a reference plane perpendicular to an optical axis of the light emitting diode array module. The reference plane is arranged at a defined distance to the light emitting diode array module.

The color of one of the LED structures may be preferably be characterized by the color temperature, correlated color temperature and the like. Especially the correlated color temperature may be preferred to characterize a LED module emitting white light.

Classic high-power LED structures are simple surface emitting light sources. However, these structures are getting smaller as time progresses, which is mostly cost-driven. One of the features that are allowing for further cost-down is 5-sided emission. Where a conventional LED structure would only emit from the top, a 5-sided emitter would also emit from the sides.

Such novel emitters have advantages in cost, but also in design flexibility. One could for example envisage a close-packed array of these emitters to achieve a very high-density high-flux emitter array.

Because of the 5-sided emission, light exiting the side of an emitter has a reasonable chance of entering a neighboring LED. The light entering its neighbor will interact with the neighboring LED which can result in a change of color and/or a change of flux. Such a change may be caused by phosphor interaction in the second LED structure and/or absorption of light in the second LED structure.

An LED structure at the edge of an array will therefore be affected less than an LED structure in the middle of the array.

This may result in:

-   -   An array with a total flux and average color point that is         different from the LEDs when used in isolation.     -   Over the array, the flux and color will vary. Color variation         over the array is unwanted as it may result in non-uniform spot         lighting.

The LED array module described above avoids or at least reduces the problem of color (flux) variation by taking into account the influence of neighboring LED structures in the LED array module. The LED structures are characterized by different (e.g. first, second, third, fourth etc.) colors or correlated color temperatures and optionally first, second, third, fourth fluxes which are combined in a way that the interaction between the LED structures is taking into account in order to provide the predefined color point and optionally flux distribution. The predefined correlated color temperature distribution may, for example, be a homogeneous or uniform correlated color temperature distribution or it may be a non-uniform color point distribution (e.g. a cool white correlated color temperature in a center and a warm white correlated color temperature at a border of the light distribution provided by means of the LED array module).

The correlated colors or color temperature of the LED structures and/or the fluxes may be chosen based on the binning of the different LED structures. That means that LED structures with, for example, different correlated color temperatures and/or fluxes are combined, wherein the difference of the correlated color temperatures and/or fluxes is caused by variations in the production process of the LED structures. Alternatively, LED structures with different semiconductor layers (e.g. composition of active layer) and/or different light conversion structure may be combined in order to enable the predefined distribution of the color and especially the correlated color temperature and/or fluxes of the LED array module.

The first, second, third etc. color or correlated color temperature and/or fluxes of the LED structures refers to the color, or correlated color temperature of an isolated LED structure without any interaction with neighboring LED structures.

At least the first light emitting diode structure of the plurality of light emitting diode structures may be further characterized by a first flux. At least a third light emitting diode structure of the plurality of light emitting diode structures may be characterized by a third flux. The first flux, the third flux and the optical cross talk between the light emitting diodes may be arranged to provide the predefined light distribution in the reference plane. The third LED structure may be the same as the second LED structure or a different LED structure. The third LED structure may be further characterized by a third color or correlated color temperature different than the first and/or second color or correlated color temperature.

The predefined light distribution may comprise a predefined color point temperature distribution. The first correlated color temperature and the second correlated color temperature may be arranged to at least partly compensate the optical cross talk between the light emitting diode structures such that a homogeneity of the predefined color point temperature distribution is increased.

The optical cross talk between the LED structures may cause an unintended shift of the correlated color temperature of neighboring LED structures. This unintended shift may be compensated by providing 2, 3, 4 or more LED structures with different correlated color temperatures.

The light emitting diode structures may be arranged to emit primary light and secondary light. The primary light is characterized by a first center wavelength in a first wavelength range. The secondary light is characterized by a second center wavelength in a second wavelength range. The second wavelength range is in a longer wavelength range than the first wavelength range. The at least first correlated color temperature and the at least second correlated color temperature are determined based on a probability that a light emitting diode structure receives primary light from one or more light emitting diode structures encompassing the light emitting diode structure.

The probability may be determined based on a number of the light emitting diode structures encompassing the light emitting diode structure.

The probability may alternatively or in addition be determined based on a distance between the light emitting diode structures encompassing the light emitting diode structure and the light emitting diode structure.

The probability may alternatively or in addition be determined based on a relative position of the light emitting diode structures encompassing the light emitting diode structure with respect to the light emitting diode structure.

The probability of receiving light and especially primary or secondary light is in general determined by the illumination pattern of each single LED structure and the geometric arrangement of the LED structures within the LED array module. Symmetry of the LED structures within the LED array module, varying distances lengths of common border between neighboring LED structures influence the probability that, for example, primary light is received by a light conversion structure of a neighboring (encompassing) LED structure. Furthermore, the arrangement of the LED structures may influence emission of secondary light which may be emitted after conversion of primary light received from a neighboring LED structure. In addition there may be optical structures especially at the border of a LED array module which may be arranged to reflect, for example, primary light emitted by LED structures at the border back to the emitting LED structure or a neighboring LED structure of the emitting LED structure. The optical structure or structures may especially be arranged to approximately mimic a neighboring LED. The optical structure may have in this case the effect that, for example, primary light emitted by a LED structure is reflected such that it appears for the emitting LED structure and neighboring LED structures that there is one or more LED structure at the position of the optical structure. The optical structure or structures provide a kind of image of the LED structures at the border of the LED array module.

A correlated color temperature of the light emitting diode structure encompassed by the light emitting structures may be higher the higher the probability of receiving primary light from the encompassing light emitting diode structures is.

The probability of receiving, for example, primary light from LED structures by means of a light conversion structure (e.g. phosphor layer) and the probability of conversion of this primary light to secondary light determine the amount of additional secondary light which is emitted by the light conversion structure of the respective LED structure. It may therefore be necessary to shift the correlated color temperature of an LED structure with a high probability of emitting additional secondary light based on the primary light received from encompassing LED structures to higher correlated color temperatures. The higher correlated color temperature may be chosen such that the ratio between primary light and secondary light emitted by the LED structure encompassed by the other LED structures is essentially the same as a ratio of the primary light and secondary light emitted by the encompassing LED structures (taking into account the cross talk between all neighboring LED structures).

The predefined correlated color temperature distribution may be flat within a defined distance from the optical axis. The first, second, third, fourth or more different correlated color temperatures of the LED structures may be used to extend the sector of uniform correlated color temperature of a lighting pattern provided by a LED array structure. The predefined correlated color temperature distribution may in this case be flat in the reference plane around the optical axis. The different (lower) correlated color temperature of LED structures at the border of the array may extend the distance from the optical axis in the reference plane in which the predefined correlated color temperature distribution is flat.

The light emitting diode array module may comprise a multitude of light emitting diode structures arranged in a regular pattern. The regular pattern of light emitting diode structures comprises a central area and a border area. A correlated color temperature of light emitting diode structures comprised by the border area is arranged to at least partly compensate the optical cross talk in accordance with a correlated color temperature distribution provided by light emitting diode structures comprised by the central area.

The light emitting structures of the LED array module may be characterized by, for example sub arrays with different emission characteristics. The correlated color temperature of the LED array module in the central area may, for example, be determined by the intensity provided by the different sub arrays of LED structures. LED structures comprised by the border area of the LED array module are characterized by different correlated color temperatures of the respective sub array in comparison to the central area in order to compensate changes of the correlated color temperature caused by varying optical cross talk caused by the geometric arrangement of encompassing LED structures as described above.

According to a further aspect a lighting device is provided. The lighting device comprises one, two, three or more light emitting diode array modules as described above. The lighting device further comprises at least one optical device being arranged to distribute light emitted by the at least one light emitting diode array module. The optical device may be a single lens or a complex arrangement of lenses, apertures and the like.

According to a further aspect a method of emitting light with a homogeneous color point distribution by means of a light emitting diode array module comprising a plurality of light emitting diode structures is provided. The method comprises the steps of:

-   -   emitting light of a first correlated color temperature by means         of at least a first light emitting diode structure of the         plurality of light emitting diode structures such that there is         an optical cross talk with at least a second light emitting         diode structure,     -   emitting light of a second correlated color temperature         different than the first correlated color temperature by means         of at least the second light emitting diode structure of the         plurality of light emitting diode structures such that there is         an optical cross talk with at least the first light emitting         diode structure, wherein the first correlated color temperature         and the second correlated color temperature are arranged to at         least partly compensate the optical cross talk between the light         emitting diode structures such that a homogeneity of a         predefined correlated color temperature distribution in a         reference plane perpendicular to an optical axis of the light         emitting diode array module is increased.

It shall be understood that the light emitting diode array module of any one of claims 1-10 and the method of claim 11 have similar and/or identical embodiments, in particular, as defined in the dependent claims.

It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

Further advantageous embodiments are defined below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

The invention will now be described, by way of example, based on embodiments with reference to the accompanying drawings.

In the drawings:

FIG. 1 shows a principal sketch of a light emitting diode structure

FIG. 2 shows a principal sketch of a light emitting diode array

FIG. 3 shows a principal sketch of a first embodiment of a LED array module

FIG. 4 shows a principal sketch of a second embodiment of the LED array module

FIG. 5 shows a principal sketch of a third embodiment of the LED array module

FIG. 6 shows a principal sketch of a cross-section of a fourth embodiment of the LED array module

FIG. 7 shows a first embodiment of a predefined correlated color temperature distribution

In the Figures, like numbers refer to like objects throughout. Objects in the Figures are not necessarily drawn to scale.

DETAILED DESCRIPTION OF EMBODIMENTS

Various embodiments of the invention will now be described by means of the Figures.

FIG. 1 shows a principal sketch of a cross-section of a light emitting diode (LED) structure 10. The LED structure 10 comprises a n-layer 3 which can be electrically contacted by means of n-contact 5. The n-layer 3 is followed by active layer 4. The active layer 4 may comprise a Quantum Well structure which is arranged to emit light with a wavelength which is determined by the composition of the active layer (e.g., AlInGaN). The active layer 4 is embedded or sandwiched between the n-layer 3 and a p-layer 7. The p-layer 7 can be electrically contacted by means of p-contact 9. The arrangement of n-layer 3, active layer 4, p-layer 9, n-contact 5 and p-contact 9 build a LED die. There may be further support layers which are not shown. A light conversion structure 1 is attached to a top surface of the n-layer 3 which is opposite to surface of the n-layer 3 attached to the active layer 4. The top surface of the n-layer 3 is the light emitting surface of the LED die. The light conversion structure 1 may comprise a phosphor like a Cerium doped phosphor garnet (YAG:Ce). The light conversion structure 1 is arranged to convert primary light 11 (e.g. blue light) emitted by the active layer 4 to secondary light 12 (e.g. yellow light) characterized by a longer wavelength than the primary light 11. A predefined part of the primary light 11 passes light conversion structure 1 without being converted such that the LED structure emits a mixture of primary light 11 and secondary light 12 (white light). The LED structure 10 is arranged to emit at least a major part of the light via a top surface and the side surfaces of the light conversion structure 1, wherein the top surface is opposite to the surface of the light conversion structure 1 which is attached to the n-layer 3. A LED structure 10 with a rectangular or quadratic cross-section perpendicular to the cross-section shown in FIG. 1 comprises therefore five light emission surfaces.

Alternatively, a kind of lid comprising the phosphor material may be arranged around the LED die of the LED structure 10 such that a mixture of primary and secondary light is emitted by means of different sides of the LED structure 10. Furthermore, the LED structure 10 may be embedded in a transparent light distribution structure which is arranged to emit light and essentially all directions of the semi-sphere in the direct direction of light emission of the LED structure 10.

FIG. 2 shows a principal sketch of a cross-section of a light emitting diode array 30. The light emitting diode array 30 comprises a number of LED structures 10 (three arc shown in the cross-section) attached to a submount 20. The submount 20 comprises a submount chip 21 on which the LED structures 10 are mounted and electrical contact pads 23 by means of which the n-contacts and p-contacts (not shown) of the LED structures 10 can be electrically connected. The LED structures 10 emit primary (blue) light 11 and secondary (yellow) light 12. A part of the primary light 11 emitted by the left and the right LED structure 10 may hit the light conversion structure 1 of the LED structure 10 in the middle. The LED structure 10 in the middle therefore receives more primary light 11 from neighboring (or encompassing) LED structures 10 than the LED structures 10 at the left and at the right. The relative fraction of secondary light emitted from the light conversion structure 1 of the LED structure 10 in the middle is therefore increased. The correlated color temperature of the LED structure 10 in the middle seems therefore to be lower than the correlated color temperature of the LED structures on the left and the right side provided that all LED structures 10 are arranged to emit in a single arrangement, for example, white light of the same correlated color temperature. The same applies to the total flux emitted by the LED structures 10 because the LED 10 structure in the middle additionally receives more secondary light than the LED structures 10 on the left and the right side.

FIG. 3 shows a principal sketch of a top view of a first embodiment of a LED array module 30. The LED array module 30 comprises three LED structures 10 a, 10 b which are arranged along an axis (linear array) in a similar way as described with respect to FIG. 2 . A LED structure 10 a is arranged between two LED structures 10 b. The LED structure 10 a in the middle emits white light with a higher first correlated color temperature in order to compensate a color shift caused by primary light emitted by the two adjacent LED structures 10 b emitting white light with a lower second correlated color temperature in comparison to the first correlated color temperature. The second correlated color temperature is chosen such that the amount of additional converted secondary light 12 (see FIG. 2 ) caused by primary light received by the light conversion structure 1 of the LED structure 10 a in the middle is essentially compensated. The correlated color temperature distribution of the light emitting module 30 is therefore more homogeneous or uniform along the axis of the linear array. It is clear that the selection of the first and the second correlated color temperature is determined by the geometric boundary conditions such that a perfect compensation is not possible. The same principal may be used in order to compensate variations of the flux caused by the optical cross talk between neighboring LED structures 10. The flux of the LED structures 10 b at the left and the right may, for example, be higher than the optical flux of LED structure 10 a in the middle in order to improve homogeneity of the flux of LED array module 30.

FIG. 4 shows a principal sketch of a top view of a second embodiment of the LED array module 30. The LED array module 30 comprises a symmetric arrangement of LED structures 10 a, 10 b, 10 c, 10 d. The LED array module 30 comprises two symmetry axes both crossing a center point of the LED array module 30. Symmetry with respect to the first symmetry axis is in this case different than the symmetry with respect to the second symmetry axis. The LED structures 10 a, 10 b, 10 c, 10 d are arranged such that four LED structures 10 a with a first correlated color temperature are arranged in the middle of the LED array module 30. The four LED structures 10 a are encompassed by 10 LED structures 10 b, 10 c, 10 d. The correlated color temperatures of the LED structures 10 b, 10 c, 10 d is selected based on the relative position to neighboring LED structures 10 a, 10 b, 10 c, 10 d, the number of neighboring LED structures 10 a, 10 b, 10 c, 10 d and the distance(s) (the distances may, for example, be different in different directions) between the neighboring LED structures 10 a, 10 b, 10 c, 10 d. The geometry of the arrangement of the LED structures 10 a, 10 b, 10 c, 10 d in the LED array 30 determines a probability of receiving primary light from neighboring LED structures 10 a, 10 b, 10 c, 10 d. The nearer the distance, the more neighboring LED structures 10 a, 10 b, 10 c, 10 d encompass the respective LED structure 10 a, 10 b, 10 c, 10 d the higher is the probability to receive primary light from neighboring LED structures 10 a, 10 b, 10 c, 10 d. The correlated color temperature of the four LED structures 10 a in the middle is therefore the highest. It is intended to provide an essentially uniform correlated color temperature distribution across the LED array module 30 because each of the four LED structures 10 a is encompassed by seven other LED structures 10 a, 10 b, 10 c, 10 d. The second correlated color temperature of LED structures 10 b is lower than the correlated color temperature of the LED structures 10 a in the center but higher than the correlated color temperatures of LED structures 10 c, 10 b because four LED structures 10 a, 10 c, 10 d encompass LED structures 10 b such that three sides of LED structure have overlap with sides of the encompassing LED structures 10 a, 10 c, 10 d. The LED structures 10 d have a lower correlated color temperature than LED structures 10 b but at a higher correlated color temperature than LED structure 10 c being characterized by the lowest correlated color temperature of the LED array module 30.

FIG. 5 shows a principal sketch of a top view of a third embodiment of the LED array module 30. LED array module 30 comprises in this case two sub arrays of LED structures, which are arranged in a checkerboard pattern. The LED structures 17 of the first sub array (bright squares) are arranged to emit light of a first characteristic. The LED structures of the second sub array (dark squares) are arranged to emit light of a second characteristic. Each sub array 17, 18 can be controlled independently from the other sub array. The LED structures 17 of the first sub array may, for example, be arranged to emit light with a first color (e.g. blue). The LED structures 18 of the second sub array may, for example, be arranged to emit light with a second color (e.g yellow). The color of the light emitted by the LED array module 30 can therefore be controlled by means of the relative intensities provided by the two sub arrays. The general problem as discussed with respect to FIGS. 2, 3 and 4 remains the same. The LED array module 30 comprises a central area 16 wherein the LED structures 17, 18 of the central area 16 are each encompassed by the same number and kind of LED structures 17, 18. The LED array module 30 further comprises a border area 15 in which the number of encompassing LED structures 17, 18 depends on the position within the border area 15. The color of the LED structures 17, 18 of the border area 15 are therefore different than the color of the LED structures 17, 18 of the corresponding central area 16 in order to compensate the different optical crosstalk between the LED structures 17, 18. The color of the LED structures 17, 18 of the border area 15 essentially depends on the number of LED structures 17, 18 encompassing the respective LED structure 17, 18. The area of the LED array module 13 appearing to emit light of the same color and correlated color temperature is thus increased. The border area 15 and the central area 16 are separated by a small gap in FIG. 5 in order to simplify identification of LED structures 17, 18 of the central area 16 and the border area 15. There is no such a gap in the real LED array module 30.

FIG. 6 shows a principal sketch of a cross-section of a fourth embodiment of the LED array module 30. The LED array module comprises an array of 5×6 LED structures 10. The cross section shows six LED structures 10 in the third of the five lines of LED structures 10 which are arranged in a regular quadratic pattern. The LED structures 10 are attached to a submount 20 comprising a submount chip 21 and electrical contact pads 23 as discussed with respect to FIG. 2 . The LED array module 30 comprises an optical axis 50 which is arranged in the middle of the 5×6 LED structures 10. Each of the LED structures 10 emits mixed light 13 comprising primary light 11 and secondary light 12 as discussed with respect to FIG. 2 . The mixed light 13 overlaps in reference plane 40 which may, for example, be arranged in a distance preferably between 5 mm and 10 mm in order to detect the impact of the LED structures 10 comprised by the LED module 30. The correlated color temperature of the LED structures 10 of the central area of the LED array module 30 is higher in comparison to the correlated color temperature of the LED structures 10 of the border area of the LED array module 30. The LED structures 10 at the four corners of the LED array module 30 are characterized by the lowest correlated color temperature because these LED structures 10 are encompassed by the lowest number of encompassing LED structures 10.

FIG. 7 shows the predefined correlated color temperature distribution 65 of the LED array module 30 shown in FIG. 6 along an axis of reference plane 40. The axis crosses the optical axis 50 and is arranged along the line defined by the LED structures 10 shown in FIG. 6 . The abscissa 61 shows the distance to the optical axis 50 in the reference plane 40 and the ordinate 62 shows the correlated color temperature along the axis in the reference plane 40. The predefined correlated color temperature distribution 65 is essentially constant or flat within a predefined range around the optical axis 50 in the reference plane 40. The predefined range within the reference plane 40 is determined by the illumination pattern provided by each LED structure 10, the geometric orientation of the LED structures 10 within the LED array module 30 and the compensation of the optical cross talk by means of the different correlated color temperature of LED structures 10 in the border area of the LED array module 30.

Although the disclosure mainly speaks of correlated color temperature to describe the color of LED structures 10, the invention is not limited to colors of a black body radiator. A person skilled in the art will understand that the invention holds for color compensation in the full color space. Typically, the colors mentioned in the disclosure will be along the phosphor load line(s), i.e. the colors one can create by changing the concentration of phosphor in light conversion structure 1 of the corresponding LED structure 10.

While the invention has been illustrated and described in detail in the drawings and the foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art and which may be used instead of or in addition to features already described herein.

Variations to the disclosed embodiments can be understood and effected by those skilled in the art, from a study of the drawings, the disclosure and the appended claims. In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality of elements or steps. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope thereof.

LIST OF REFERENCE NUMERALS

-   -   1 light conversion structure     -   3 n-layer     -   4 active layer     -   5 n-contact     -   7 p-layer     -   9 p-contact     -   10 light emitting diode (LED) structure     -   10 a LED structure with first correlated color temperature     -   10 b LED structure with second correlated color temperature     -   10 c LED structure with third correlated color temperature     -   10 d LED structure with fourth correlated color temperature     -   11 primary light     -   12 secondary light     -   13 mixed light     -   15 light emitting diode structure of border area     -   16 light emitting diode structure of central area     -   17 LED structure of first sub array     -   18 LED structure of second sub array     -   20 submount     -   21 submount chip     -   23 electrical contact pads     -   30 light emitting diode (LED) array module     -   40 reference plane     -   50 optical axis     -   61 distance to optical axis in reference plane     -   62 correlated color temperature in reference plane     -   65 correlated color temperature distribution in reference plane 

The invention claimed is:
 1. An apparatus, comprising: a plurality of light-emitting diodes (LEDs) arranged as an LED array, the plurality of LEDs being distributed between a central group of LEDs and a border group of LEDs that surrounds the central group of LEDs, the central group of LEDs being arranged in a two-dimensional subarray, the central group of LEDs including central blue LEDs that are configured to emit central blue light and central yellow LEDs that are configured to emit central yellow light such that, when observed at a reference plane separated from the LED array, the central blue light and the central yellow light combine to appear as central white light having a central correlated color temperature, and the border group of LEDs including border blue LEDs that are configured to emit border blue light and border yellow LEDs that are configured to emit border yellow light such that, when observed at the reference plane, the border blue light and the border yellow light combine to appear as border white light having a border correlated color temperature that is different from the central correlated color temperature.
 2. The apparatus of claim 1, wherein: the central blue LEDs and the central yellow LEDs are arranged in a checkerboard pattern in the LED array; and the border blue LEDs and the border yellow LEDs are arranged in a checkerboard pattern in the LED array.
 3. The apparatus of claim 1, wherein: each of the central blue LEDs is configured to emit light having a same central blue intensity; each of the central yellow LEDs is configured to emit light having a same central yellow intensity; each of the border blue LEDs is configured to emit light having a same border blue intensity; each of the border yellow LEDs is configured to emit light having a same border yellow intensity; and a ratio of the central blue intensity to the central yellow intensity differs from a ratio of the border blue intensity to the border yellow intensity.
 4. The apparatus of claim 1, wherein: each LED in the central group is fully surrounded by adjacent LEDs in the LED array; and each LED in the border group is only partially surrounded by adjacent LEDs in the LED array.
 5. The apparatus of claim 1, wherein: the array of LEDs is a two-dimensional rectilinear array; each LED in the central group is surrounded by four directly adjacent LEDs and four diagonally adjacent LEDs in the LED array; and each LED in the border group is surrounded by fewer than four directly adjacent LEDs or fewer than four diagonally adjacent LEDs in the LED array.
 6. The apparatus of claim 1, wherein: the LED array is a two-dimensional array that extends in a first plane that is generally parallel to the reference plane; each LED in the array is configured to emit light from a first emission surface oriented generally parallel to the first plane and from at least one second emission surface oriented substantially orthogonal to the first emission surface; and the LEDs of the array are arranged such that the at least one second emission surface of an LED is positioned to receive light from a second emission surface of at least another LED in the array.
 7. The apparatus of claim 6, wherein light emitted from a second emission surface of a first LED of the array is configured to interact with a phosphor of a second LED of the array.
 8. The apparatus of claim 6, wherein central blue light emitted from a second emission surface of a first central blue LED is configured to be absorbed by a phosphor of a first central yellow LED.
 9. The apparatus of claim 6, wherein central blue light emitted from a second emission surface of a first central blue LED is configured to be absorbed by a phosphor of a first border yellow LED.
 10. The apparatus of claim 6, wherein border blue light emitted from a second emission surface of a first border blue LED is configured to be absorbed by a phosphor of a first border yellow LED.
 11. The apparatus of claim 6, wherein border blue light emitted from a second emission surface of a first border blue LED is configured to be absorbed by a phosphor of a first central yellow LED.
 12. A method for providing light, comprising: electrically powering a plurality of light-emitting diode (LEDs) arranged as an LED array, the plurality of LEDs being distributed between a central group of LEDs and a border group of LEDs that surrounds the central group of LEDs, the central group of LEDs being arranged in a two-dimensional subarray, the central group of LEDs including central blue LEDs and central yellow LEDs, the border group of LEDs including border blue LEDs and border yellow LEDs; emitting central blue light from the central blue LEDs; emitting central yellow light from the central yellow LEDs such that, when observed at a reference plane separated from the LED array, the central blue light and the central yellow light combine to appear as central white light having a central correlated color temperature; emitting border blue light from the border blue LEDs; and emitting border yellow light from the border yellow LEDs such that, when observed at the reference plane, the border blue light and the border yellow light combine to appear as border white light having a border correlated color temperature that is different than the central correlated color temperature.
 13. The method of claim 12, wherein: the central blue LEDs and the central yellow LEDs are arranged in a checkerboard pattern in the LED array; and the border blue LEDs and the border yellow LEDs are arranged in a checkerboard pattern in the LED array.
 14. The method of claim 12, wherein: the central blue LEDs emit light having a same central blue intensity; the central yellow LEDs emit light having a same central yellow intensity; the border blue LEDs emit light having a same border blue intensity; the border yellow LEDs emit light having a same border yellow intensity; and a ratio of the central blue intensity to the central yellow intensity differs from a ratio of the border blue intensity to the border yellow intensity.
 15. The method of claim 12, wherein at least some of the LEDs of the LED array are monolithic devices disposed on a single substrate.
 16. The method of claim 12, wherein: each LED in the central group is fully surrounded by adjacent LEDs in the LED array; and each LED in the border group is only partially surrounded by adjacent LEDs in the LED array.
 17. The method of claim 12, wherein: the array of LEDs is a two-dimensional rectilinear array; each LED in the central group is surrounded by four directly adjacent LEDs and four diagonally adjacent LEDs in the LED array; and each LED in the border group is surrounded by fewer than four directly adjacent LEDs or fewer than four diagonally adjacent LEDs in the LED array.
 18. An apparatus, comprising: a plurality of light-emitting diode (LEDs) arranged as a two-dimensional rectilinear LED array, the plurality of LEDs being distributed between a central group of LEDs and a border group of LEDs that surrounds the central group of LEDs, the central group of LEDs being arranged in a two-dimensional subarray, each LED in the central group being surrounded by four directly adjacent LEDs and four diagonally adjacent LEDs in the LED array, each LED in the border group being surrounded by fewer than four directly adjacent LEDs or fewer than four diagonally adjacent LEDs in the LED array, the central group of LEDs including central blue LEDs that are configured to emit central blue light and central yellow LEDs that are configured to emit central yellow light such that, when observed at a reference plane separated from the LED array, the central blue light and the central yellow light combine to appear as central white light having a central correlated color temperature, the central blue LEDs and the central yellow LEDs being arranged in a checkerboard pattern in the LED array, and the border group of LEDs including border blue LEDs that are configured to emit border blue light and border yellow LEDs that are configured to emit border yellow light such that, when observed at the reference plane, the border blue light and the border yellow light combine to appear as border white light having a border correlated color temperature that is different than the central correlated color temperature, the border blue LEDs and the border yellow LEDs are arranged in a checkerboard pattern in the LED array.
 19. The apparatus of claim 18, wherein: the LED array is a two-dimensional array that extends in a first plane that is generally parallel to the reference plane; each LED in the array is configured to emit light from a first emission surface oriented generally parallel to the first plane and from at least one second emission surface oriented substantially orthogonal to the first emission surface; the LEDs of the array are arranged such that the at least one second emission surface of an LED is positioned to receive light from a second emission surface of at least another LED in the array; light emitted from a second emission surface of a first LED of the array is configured to interact with a phosphor of a second LED of the array; central blue light emitted from a second emission surface of a first central blue LED is configured to be absorbed by a phosphor of a first central yellow LED; central blue light emitted from a second emission surface of a first central blue LED is configured to be absorbed by a phosphor of a first border yellow LED; border blue light emitted from a second emission surface of a first border blue LED is configured to be absorbed by a phosphor of a first border yellow LED; and border blue light emitted from a second emission surface of a first border blue LED is configured to be absorbed by a phosphor of a first central yellow LED. 